Industrial processes for production of cellulose-rich pulps from harvested wood are well-known and typically involve the steps of physical disruption of wood into smaller pieces and particles followed by chemical digestion under elevated temperatures and pressures to dissolve and separate the lignins from the constituent cellulosic fibrous biomass. After digestion has been completed, the solids comprising the cellulosic fibrous pulps are separated from the spent digestion liquids which commonly referred to as black liquors and typically comprise organic solvents, solubilized lignins, solid and particulate monosaccarides, oligosaccharides, polysaccharides and other organic compounds released from the wood during the chemical digestion. The cellulosic fibrous pulps are typically used for paper manufacturing while the black liquors are usually processed to recover the heat value in the soluble lignins and for recovery, purification and recycling of the solvents.
During the past two decades, those skilled in these arts have recognized that lignocellulosic materials including harvested gymnosperm and angiosperm substrates exemplified by chips and sawdust, woody undercuttings and debris from forest plantations, annual and perennial field crop residues, bagasse and other like types of herbaceous fibrous biomass, waste paper wood products, waste materials and debris from wood-processing operations, and the like, can be potentially fractionated using biorefining processes incorporating organosolv digestion systems, into multiple useful component parts that can be separated and further processed into high-value products such as fuel ethanol, lignins, furfural, acetic acid, purified monosaccharide sugars among others (Pan et al., 2005, Biotechnol. Bioeng. 90: 473-481; Pan et al., 2006, Biotechnol Bioeng. 94: 851-861; Berlin et al., 2007, Appl. Biochem. Biotechnol. 136-140:267-280; Berlin et al., 2007, J. Chem. Technol Biotechnol. 82: 767-774). Organosolv pulping processes and systems for lignocellulosic feedstocks are well-known and are exemplified by the disclosures in U.S. Pat. Nos. 4,941,944; 5,730,837; 6,179,958; and 6,228,177. Although it appears that biorefining using organosolv systems has considerable potential for large-scale fuel ethanol production, the currently available processes and systems are not yet economically feasible because they require expensive pretreatment steps and currently produce only low-value co-products (Pan et al., 2006, J. Agric. Food Chem. 54: 5806-5813; Berlin et al., 2007, Appl. Biochem. Biotechnol. 136-140:267-280; Berlin et al., 2007, J. Chem. Technol Biotechnol. 82: 767-774).